1. Field of the Invention
The present invention relates to a reduction gear apparatus (or a speed reducer) which is used for speed reduction of various machines such as a concrete mixing car, a swiveling apparatus and a travelling apparatus for a hydraulic shovel, a lifting apparatus for a carriage car (or a transporting car), or the like.
2. Description of the Related Art
In various kinds of machines, there has hitherto been practiced to reduce the rotational speed of the machine by the combination of a hydraulic motor and a toothed gear type of reduction gear, or only by a hydraulic motor. The object of using this kind of speed reducing means is to obtain a low speed and high torque. For this purpose, the following arrangement has been employed. Namely, the hydraulic pump is driven by a driving source such as an engine of the machine. The delivery fluid or discharged fluid from the hydraulic pump is supplied to a swash plate type of axial piston motor "a" as shown, e.g., in FIG. 1. The rotation of a rotary shaft b of the axial piston motor "a" is transmitted to a planetary gear reduction apparatus c. In this manner, a low speed and high torque of speed reduction ratio of 15 through 130 is obtained from a rotary shaft (output shaft) d. Instead of the axial piston motor "a" a swash plate type of axial piston pump is sometimes used. Further, as shown in FIG. 2, there has also been practiced to supply a pressurized fluid from a hydraulic pump which is driven by a driving source to a multiple stroke type of radial piston motor i. This multiple stroke type of radial piston motor i is made up of a cam ring e which is disposed around an output shaft d and which has a cam surface with a radially projected and recessed inner peripheral surface, and pistons h which move, along the cam surface, radially into, and out of, cylinders g of a cylinder block f which are mounted on the output shaft d. Low speed and high toque can thus be obtained.
In the above-described conventional reduction gear apparatus which is made up solely of the hydraulic motor, when the torque to be outputted becomes large, the hydraulic motor also becomes large and of special construction. It thus requires a large space for mounting. The weight also becomes large, with the result that it is no longer suitable for use in a vehicle. In the apparatus in which the axial piston motor and the planetary gear are combined, on the other hand, the axial piston motor is designed to obtain a high speed and low torque. Therefore, in order to obtain the predetermined low speed and high torque, the reduction ratio is set to be about 15 through 130. In order to obtain this range of gear ratios, there will be required a planetary gear mechanism of two to three stages of speed reduction. As a result, as shown in FIG. 1, the total length becomes large and the weight also becomes large, resulting in a higher cost.
In view of the above-described disadvantages in the conventional apparatuses, the present invention has an object of providing a reduction apparatus in which a low speed and high torque can be obtained and which is small in size and light in weight and can be manufactured at a smaller cost.